High pressure liquid air power and storage

ABSTRACT

Apparatus, systems, and methods store energy by liquefying a gas such as air, for example, and then recover the energy by regasifying the liquid and combusting or otherwise reacting the gas with a fuel to drive a heat engine. The process of liquefying the gas may be powered with electric power from the grid, for example, and the heat engine may be used to generate electricity. Hence, in effect these apparatus, systems, and methods may provide for storing electric power from the grid and then subsequently delivering it back to the grid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationPCT/US2016/054152 titled “High Pressure Liquid Air Power And Storage”and filed Sep. 28, 2016. PCT/US2016/054152 claims benefit of priority toU.S. Provisional Patent Application No. 62/244,407 titled “High PressureLiquid Air Power And Storage” and filed Oct. 21, 2015; U.S. ProvisionalPatent Application No. 62/244,648 titled “High Pressure Liquid Air PowerAnd Storage” and filed Oct. 21, 2015; U.S. Provisional PatentApplication No. 62/357,216 titled “High Pressure Liquid Air Power AndStorage” and filed Jun. 30, 2016; U.S. Provisional Patent ApplicationNo. 62/364,781 titled “High Pressure Liquid Air Power And Storage” andfiled Jul. 20, 2016; and U.S. Provisional Patent Application No.62/379,970 titled “High Pressure Liquid Air Power And Storage” and filedAug. 26, 2016; each of which is incorporated herein by reference in itsentirety.

This application is related to U.S. patent application Ser. No.14/546,406 titled “Liquid Air Power and Storage” and filed Nov. 18,2014, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates generally to storing energy by liquefying air oranother gas or gaseous mixture, and subsequently recovering storedenergy upon regasifying the liquid.

BACKGROUND

The electric power system comprises generation, transmission, anddistribution assets, which deliver power to loads. With the introductionof renewable resources, the electric power system faces a number ofconstraints which favor the addition of storage assets.

The principal constraint on an interconnected grid is the need tomaintain the frequency and voltage by balancing variations in generationand demand (load). Failure to maintain the voltage or frequency withinspecifications causes protective relays to trip in order to protectgenerators, transmission and distribution assets from damage. Because ofthe interconnected dynamic electrical grid, under/over-frequency orunder/over-voltage trips can cause a cascade of other trips, potentiallyleading to widespread blackouts.

Traditionally, electric utilities or the independent system operatorsmanaging electrical grids maintain a power generation reserve marginthat can respond to changes in load or the loss of a generating unit ortransmission line serving the load. These reserves are managed andscheduled using various planning methods, including day-ahead forecasts,dispatch queues that may be ordered based on generation cost, andgeneration ramp-rates, transmission constraints, outages, etc. Thespinning generation units, that is, those that are operating, thenrespond to generation load control signals.

Many renewable resources are intermittent in nature, including windfarms, central station solar thermal or solar photovoltaic (PV) plants,and distributed photovoltaic systems including those on rooftops. Thesecan produce power only when the resource is available, during daylightfor solar, and when the wind is blowing for wind, leading to seasonaland diurnal production variations, as well as short-term fluctuationsdue to calms, gusts, and clouds. Gusts that exceed wind turbine ratingsmay cause them to trip with a sudden loss of full generation capacity.Deployment of these renewable systems as both central and distributedgenerating resources results in fluctuations in both the generation ofpower to be transmitted and the demand for power, since the distributedPV offsets load.

Base load is usually provided by large central station nuclear,hydroelectric or thermal power plants, including coal-fired steam plants(Rankine cycle) or gas-fired Combined Cycle Combustion Turbine plants(open Brayton air cycle with closed Rankine steam bottoming cycle).Base-load units often have operating constraints on their ramp rates(Megawatts per minute) and Turn-Down (minimum Megawatts), and startupfrom cold steel to rated load requires several hours to several daysdepending on the type and size of generating asset. Accordingly, adifferent class of load following power plants is also deployed in theelectric power system, to complement the base load units. Generally,these load following units are less efficient in converting thermalenergy to electrical energy.

This conversion efficiency is often expressed as a Heat Rate with unitsof thermal energy needed to produce a kilowatt-hour (kw-hr) ofelectricity [British Thermal Unit (BTU) per kw-hr in the U.S.,kiloJoules (kJ) per kw-hr elsewhere]. The thermal equivalent of work is3413 BTU/kw-hr or 3600 kJ/kw-hr, which represents 100% efficiency.Modern combined cycle power plants at full load rated conditions mayhave heat rates as low, for example, as 6000 kJ/kw-hr. Modern gasturbine peaking plants (e.g., General Electric LM6000-PC SPRINT) canachieve a full load rated condition heat rate of 9667 kJ/kw-hr based onHigher Heating Value (HHV). It is important to note that gas turbineheat rates increase rapidly away from rating conditions, and at partload in hot conditions the actual heat rate may be twice the rated HeatRate.

It is of course desired to deliver electricity to customers at thelowest possible cost. This cost includes the amortization and profit oninvested capital, the operating and maintenance (O&M) expense, and thecost of fuel. The capital amortization (and return on capital, in thecase of regulated generators) is applied to the capacity factor(fraction of rated generation) to arrive at the price ($ perMegawatt-hour) associated with the fixed capital expense. The Heat Ratemultiplied by the fuel cost determines the contribution of the variablefuel consumption to the electricity price. The O&M expenses generallyhave some combination of fixed and variable expenses, but areinsignificant compared to capital and fuel for central station plants.Generating units have different mixes of fixed and variable expenses,but presumably were believed to be economic at the time they wereordered.

In order to deliver low cost electricity to a customer, it is necessaryto operate the capital intensive units at high capacity, subject to fuelcost, in order to spread the capital cost across many kw-hr.Contrariwise, it is necessary to minimize the operation of units withhigh marginal operating cost (due to high Heat Rate, Fuel Cost or O&M).This was indeed the planning assumption for procurement of the existingfleet of generators.

The Renewable resources gather ‘free’ fuel, so their cost of generationis dominated by the amortization of the capital needed to gather andconvert this energy into electricity. In order to profitably build andoperate a Renewable power plant, it should have as high a capacityfactor as may be practically realized. Similarly, the fuel-efficientbase load generation should operate at high capacity factor, both toamortize the capital expense, and because its operating characteristicsinduce higher fuel or O&M costs (per unit of generation) when operatedintermittently or at part load.

The increasing penetration of renewable generation with variablegeneration characteristics is challenging the traditional dispatch orderand cost structure of the electric generation system. In practice,utility scale solar power plants without storage are limited to CapacityFactors of about 25%, and wind farms seldom exceed 50%. This capacitymay not coincide with demand, and may be suddenly unavailable if the sunor wind resource is reduced by local weather. For example, if windresources are available at periods of low demand, base load units musteither ramp down or shut-down or the wind resource must be curtailed. Ifthe wind is not curtailed, then less efficient peaking units may beneeded to provide ramp flexibility that the large base-load units cannotprovide in case of gusts or calms. Likewise the widespread deployment ofsolar power generation is depressing the need for generation duringdaylight hours, but large ramp rates as the sun rises and sets cancurrently only be met by gas fired peaking plants. Ironically, this willresult in displacement of low-cost, high efficiency base-load units infavor of high cost, low-efficiency peaking units, with a concomitantincrease in greenhouse gas releases.

For environmental, energy security, cost certainty and other reasons,renewable energy sources are preferred over conventional sources. DemandResponse techniques, which attempt to reduce the instantaneous loaddemand to achieve balance between generation and consumption, areanalogous to a peaking generation unit. Another approach is deploymentof (e.g., large scale) energy storage systems to mediate the mismatchbetween generation and consumption.

Storage systems are alternately charged to store energy (e.g., usingelectric power), and discharged to return the energy as power to theelectric grid. The technical characteristics of energy storage systemsinclude:

-   -   the Capacity, or quantity of energy that can be stored and        returned, measured in MW-hours;    -   the Round Trip Efficiency (RTE), or fraction of the energy        delivered to the storage system that is returned to the grid;    -   the Power rating, or rate in MW at which the system can be        charged or discharged (Power is often symmetric, though this is        not necessary, or even desirable);    -   the Heat Rate, or heat added (from fuel for example) per unit of        electric energy discharged, measured in kJ per KWh (purely        electric storage would have a Heat Rate of zero);    -   the Lifetime, which is typically the number of Charge/Discharge        cycles.

Pumped Storage Hydroelectricity (PSH) employs a reversible pump-turbinewith two water reservoirs at different elevations. When excess energy isavailable, it is used to pump water from a lower to an upper reservoir,converting the electricity into potential energy. When electricity isneeded, the water flows back to the lower reservoir through ahydro-turbine-generator to convert the gravitational potential energyinto electricity. Pumped hydro storage is suitable for grid scalestorage and has been used for many decades in electrical grids aroundthe world. PSH has a Round Trip Efficiency (RTE) of 70% to 80% and canbe deployed at Gigawatt scale with many days of potential storage. Inaddition to high RTE, PSH does not generate greenhouse gases duringoperation. Deployment of PSH requires availability of suitable locationsfor the construction of dams and reservoirs, and availability of waterand its evaporative loss may be an issue in some locations.

Compressed Air Energy Storage (CAES) stores pressurized air that issubsequently expanded in an engine. Commercially deployed CAES storesthe air in large underground caverns such as naturally occurring orsolution-mined salt domes, where the weight of overburden is sufficientto contain the high pressures. The RTE for CAES may be relatively low.The 110MW McIntosh CAES plant in the US state of Alabama reportedly hasa RTE of only 27%, for example. Advanced CAES systems reportedly achieveElectric Energy Ratios of 70% or more, exclusive of fuel, and severalnear-isothermal CAES technologies are also under development withreported RTE of 50% or greater, using pressure vessels for storage.

Many energy storage technologies are being developed and deployed forend-use loads or distribution level capacities, at power levels from afew kilowatts to several megawatts. These approaches typically employbatteries with a variety of chemistries and physical arrangements.

There is a need for high efficiency energy storage that is not dependenton geological formations, and which can be deployed at scales of tens tohundreds of megawatts to complement the existing generation andtransmission assets.

SUMMARY

Apparatus, systems, and methods described in this specification storeenergy by liquefying a gas such as air, for example, and then recoverthe energy by regasifying the liquid air and expanding the gas throughone or more turbines. The turbines may drive one or more generators togenerate electricity. The process of liquefying the gas may be poweredwith electric power from the grid, for example. Hence, in effect theseapparatus, systems, and methods may provide for storing electric powerfrom the grid and then subsequently delivering it back to the grid. Theelectricity for liquefying the gas may be provided, for example, frombase load power generation or from renewable resources that wouldotherwise be curtailed, and therefore may be effectively low cost.

In one aspect, a method of storing and recovering energy comprisespressurizing liquid air or liquid air components to a pressure greaterthan or equal to about 80 atmospheres, regasifying the pressurizedliquid air or liquid air components to produce pressurized gaseous airor gaseous air components at a pressure greater than or equal to about80 atmospheres using heat produced by combusting an exhaust gas streamfrom a high pressure turbine with a gaseous fuel, expanding thepressurized gaseous air or gaseous air components through the highpressure turbine to form the exhaust gas stream, and producingelectricity with a generator driven by the high pressure turbine.

In another aspect, a method of storing and recovering energy comprisespressurizing liquid air or liquid air components to a pressure greaterthan or equal to about 80 atmospheres or greater than or equal to about120 atmospheres, regasifying the pressurized liquid air or liquid aircomponents to produce pressurized gaseous air or gaseous air componentsat a pressure greater than or equal to about 80 atmospheres or greaterthan or equal to about 120 atmospheres using heat produced by combustinguncombusted gaseous air or gaseous air components in a first exhaust gasstream from a combustion turbine with a gaseous fuel, expanding thepressurized gaseous air or gaseous air components through a highpressure turbine to form a second exhaust gas stream at a pressure ofabout 10 to about 30 atmospheres, producing electricity with a generatordriven by the high pressure turbine, combusting the second exhaust gasstream with a fuel to form a gaseous working fluid at an elevatedtemperature, expanding the gaseous working fluid through the combustionturbine to form the first exhaust gas stream, and producing additionalelectricity with a generator driven by the combustion turbine.

In another aspect, a method of storing and recovering energy comprisespressurizing liquid air or liquid air components to a pressure greaterthan or equal to about 80 atmospheres or greater than or equal to about120 atmospheres, regasifying the pressurized liquid air or liquid aircomponents to produce pressurized gaseous air or gaseous air componentsat a pressure greater than or equal to about 80 atmospheres or greaterthan or equal to about 120 atmospheres and a temperature of about −20°C. to about 100° C., further heating the pressurized gaseous air orgaseous air components using heat produced by combusting uncombustedgaseous air or gaseous air components in a first exhaust gas stream froma combustion turbine with a gaseous fuel, expanding the pressurizedgaseous air or gaseous air components through a high pressure turbine toform a second exhaust gas stream at a pressure of about 10 to about 30atmospheres, producing electricity with a generator driven by the highpressure turbine, combusting the second exhaust gas stream with agaseous fuel to form a gaseous working fluid at an elevated temperature,expanding the gaseous working fluid through the combustion turbine toform the first exhaust gas stream, and producing additional electricitywith a generator driven by the combustion turbine.

In some variations, the heat used to regasify the liquid air or liquidair components is not derived from combusting uncombusted gaseous air orgaseous air components in the first exhaust gas stream with a fuel orfrom combusting the second exhaust gas stream with a fuel, althoughthese may be heat sources for this step in other variations. In somevariations the heat used to regasify the liquid air or liquid aircomponents may be drawn from ambient sources (e.g., ambient air), forexample.

In another aspect, a method of storing and recovering energy comprisescompressing gaseous air, combusting the compressed gaseous air with agaseous fuel to form a hot gaseous working fluid, expanding the hotgaseous working fluid through a first turbine to form an exhaust gasstream, producing electricity with a generator driven by the firstturbine, pressurizing liquid air or liquid air components to a pressuregreater than or equal to about 80 atmospheres, regasifying thepressurized liquid air or liquid air components to produce pressurizedgaseous air or gaseous air components at a pressure greater than orequal to about 80 atmospheres and a temperature of about −20° C. toabout 100° C., further heating the pressurized gaseous air or gaseousair components using heat from the exhaust gas stream from the firstturbine, expanding the pressurized gaseous air or gaseous air componentsthrough a high pressure turbine, and producing electricity with agenerator driven by the high pressure turbine.

In some variations, the heat used to regasify the liquid air or liquidair components is not derived from the exhaust gas stream from the firstturbine. In some variations the heat used to regasify the liquid air orliquid air components may be drawn from ambient sources (e.g., ambientair), for example.

These and other embodiments, features and advantages of the presentinvention will become more apparent to those skilled in the art whentaken with reference to the following more detailed description of theinvention in conjunction with the accompanying drawings that are firstbriefly described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an example simple Liquid Air Power andStorage (LAPS) system.

FIG. 2 shows a block diagram of an example simple High Pressure LiquidAir Power and Storage (HPLAPS) system.

FIG. 3 shows a block diagram of an example HPLAPS as in FIG. 2 furthercomprising an air preheat and flue gas reheat subsystem.

FIG. 4 shows a block diagram of an example HPLAPS system as in FIG. 2further comprising a combustion turbine.

FIG. 5 shows a block diagram of an example HPLAPS as in FIG. 4 furthercomprising a flue gas reheat subsystem.

FIG. 6 shows a block diagram of another example HPLAPS system.

FIG. 7 shows a block diagram of an example HPLAPS system as in FIG. 6further comprising a flue gas condenser and a regasified air pre-heaterthat uses heat recovered by the flue gas condenser.

FIGS. 8A, 8B, 9A, and 9B show block diagrams of additional exampleHPLAPS systems.

DETAILED DESCRIPTION

The following detailed description should be read with reference to thedrawings, in which identical reference numbers refer to like elementsthroughout the different figures. The drawings, which are notnecessarily to scale, depict selective embodiments and are not intendedto limit the scope of the invention. The detailed descriptionillustrates by way of example, not by way of limitation, the principlesof the invention. This description will clearly enable one skilled inthe art to make and use the invention, and describes severalembodiments, adaptations, variations, alternatives and uses of theinvention, including what is presently believed to be the best mode ofcarrying out the invention. As used in this specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly indicates otherwise.

FIG. 1 shows an example simple LAPS configuration 100 similar to thosedisclosed in U.S. patent application Ser. No. 14/546,406 referred toabove. In this example power is used by liquefaction unit 110 to liquefyair for storage in cryotank 120, which is an insulated low pressurestorage vessel. For power generation, liquid air is pressurized bycryopump 130 and re-gasified in gasifier (e.g., heat exchanger) 140using heat from the exhaust of power turbine 150. Fuel (e.g., naturalgas) is combusted with the pressurized regasified air in burner 160 andthe hot combustion gas mix drives the power turbine. Water is condensedand separated from flue gas in separator 170. Steam may be mixed withthe air and fuel in burner 160. Pressurized cooling air, for examplederived from the regasified air stream, may be supplied to the hotturbine section.

Optionally, the exhaust gas from the turbine and the liquid air mayserve respectively as heat source and heat sink for a bottoming powercycle, which may be for example an organic Rankine cycle.

The simple LAPS configuration shown in FIG. 1 is analogous to a BraytonCycle combustion turbine generator, except that for LAPS the aircompression is done in steps, which include liquefying the air, followedby pumping the liquid and then regasifying. This allows the majority ofthe work required for compression to be separated in space and time fromthe useful work of power generation, thereby facilitating the use ofliquid air for energy storage.

High pressures are desired when driving a turbine because the specificwork, power per unit of working fluid, is proportional to the pressuredifference across the turbine. Although efficiency is proportional tothe temperature of the working fluid, it is technically or economicallychallenging to use a working fluid at both very high temperature andvery high pressure, because the pressure-containing materials weaken athigh temperature. For example, steam turbines operate at workingpressures of 150 to 200 bar with working fluid at 550° C. In contrastcombustion turbines may have turbine inlet temperatures of about 1400°C., but typically have far lower working pressures, on the order of 15to 20 bar. High working fluid temperatures necessitate the diversion ofsubstantial quantities of working fluid to cool the pressure boundaryand other highly stressed components. However, working fluid divertedfor cooling purposes does not produce useful work, so increasing theturbine inlet temperature faces diminishing returns.

Turbo-expanders or air turbines (together referred to herein as highpressure turbines) are available from manufacturers such as MAN, withworking pressures of, for example, up to 140 bar at 540° C. An HPLAPSsystem utilizing such a turbo expander or air turbine for turbine 150 inthe configuration shown in FIG. 1 would use a high pressure burner toheat the pressurized (e.g., 140 bar) and re-gasified air to the (e.g.,540° C.) maximum turbine inlet temperature.

Instead of using a high pressure burner, a simple HPLAPS system 200using a high pressure turbo-expander or air turbine for turbine 150could instead be implemented as shown in the example of FIG. 2. In thisconfiguration all combustion occurs at atmospheric pressure in a ductburner 180 positioned in the exhaust stream of high pressure turbine150. Liquid air is pressurized by cryopump 130 (e.g., to about 140 bar),re-gasified in gasifier 140 using heat from duct burner 180, expandedthrough high pressure turbine 150, and then exhausted from the turbineat about 1 atmosphere and combusted with a fuel (e.g., natural gas) induct burner 180 to heat regasifier 140. At start-up, a blower 190 pushesambient air into duct burner 180 where it is combusted with fuel to heatgasifier 140 and begin regasifying liquid air for expansion throughturbine 150. The flow rate and pressure of the liquid air may beadjusted (e.g., ramped up) during startup as limited by the air flowrate of blower 190, by controlling the cryopump speed or recycling afraction of the liquid air to cryotank 120. The liquid air pressure mayhave a transient ramp-up pressure of greater than or equal to about 5atmospheres during start-up, for example. Additional fuel may be addedas exhaust air from turbine 150 is mixed with air from blower 190. Afterstartup the duct burner fuel flow may be controlled to maintain thespecified turbine inlet temperature. Blower 190 may be shut down afterstart-up, or optionally continue to run.

In an HPLAPS system configured as in FIG. 2 the exhaust from the turbinemay be cold enough to warrant preheating before it enters the ductburner. In addition, to extract all or nearly all of the latent heat ofcondensation from water vapor in the exhaust stream exiting the ductburner and transfer that heat to the regasified liquid air, gasifier 140may be configured and operated to chill the exhaust from the duct burnerto near 0° C. To avoid a visible plume at the stack, the flue gas can bereheated after the gasifier.

Such pre-heating and reheating can be accomplished, for example, asshown in HPLAPS system 300 of FIG. 3. In this example, heat rejectedfrom liquefaction unit 110 warms a heat transfer fluid as it passesthrough heater (e.g., heat exchanger) 200. The warmed heat transferfluid, which may optionally be stored in warm tank 210, is thencirculated through air heater 220 to reheat the flue gas and throughpreheater 230 to preheat the exhaust stream from turbine 150. Afterpassing through preheater 230, the now cooled heat transfer fluid mayoptionally be stored in cold tank 240 before passing through air chiller(e.g., heat exchanger) 250, where it precools air to be liquefied in theliquefaction unit, and then cycle again through heater 200. The coldtank 240 and warm tank 210 provide energy storage within the LAPSprocess to improve the process efficiency, in contrast to the cryotank120, which stores energy from outside the LAPS process. The heattransfer fluid may be water or a coolanol, for example, such as asolution of water and ethylene glycol, commonly known as anti-freeze.Any other method of preheating air before it enters the duct burnerand/or reheating flue gas may also be used. Some variations may preheatair to the duct burner but not reheat flue gas. Other variations mayreheat flue gas, but not preheat air to the duct burner.

Table 1 below shows the estimated performance of the HPLAPS system 300of FIG. 3 for example operating parameters. Assuming that the turbineexhaust air is preheated to 20.0° C., the preheat duty of 1.9 MW couldhelp to reduce the power requirement of the air liquefaction system byabout 8%.

FIG. 4 shows an example HPLAPS system that combines the high pressureturbine of FIG. 2 and FIG. 3 with the combustion turbine of FIG. 1. InHPLAPS system 400 of FIG. 4, liquid air is pressurized by cryopump 130(e.g., to about 140 bar), re-gasified in gasifier 140 using heat fromduct burner 180, expanded through high pressure turbine 150 to generatepower, and exhausted from the high pressure turbine 150 at the (e.g.,15-20 bar) inlet pressure for combustion turbine 260. The mediumpressure air exhausted from high pressure turbine 150 is combusted inburner 270 with a fuel (e.g., natural gas), and then the hot combustiongas mix (e.g., at about 1112° C.) is expanded through combustion turbine260 to generate additional power. Uncombusted air in the exhaust streamfrom combustion turbine 260, optionally mixed with additional airprovided by blower 190, is then combusted with a fuel (e.g., naturalgas) in duct burner 180 to raise its temperature (e.g., to about 720°C.) and heat gasifier 140. At start-up, blower 190 pushes ambient airinto duct burner 180 where it is combusted with fuel to heat gasifier140 and begin regasifying liquid air for expansion through turbine 150.After startup the duct burner fuel flow may be controlled to maintainthe specified turbine inlet temperature for the high pressure turbine.Blower 190 may be shut down after start-up, or optionally continue torun. As shown in HPLAPS system 500 of FIG. 5, the HPLAPS configurationof FIG. 4 may comprise a flue gas reheating system as shown in FIG. 3.

Table 1 shows the estimated performance of the HPLAPS system 400 of FIG.4 for example operating parameters.

An advantage of the example configurations shown in FIG. 4 and FIG. 5 isthat although they operate with both a high total pressure drop (e.g.,140 bar) and at high temperature (e.g., 1112° C.), no single expansionstep occurs at both high pressure and high temperature. This facilitatesthe mechanical design of the expander casings, permitting pressurecontaining parts to be made of thinner walls to reduce cost and thermalstress, thereby also reducing startup time. As shown in Table 1 below,the combination of high pressure air expansion and high temperature airexpansion results in substantially increased power output andefficiency. Another advantage of the example configurations shown inFIG. 4 and FIG. 5 is that the pressure and temperature at the inlet tocombustion turbine 260 is lower than in the examples shown in therelated U.S. patent application Ser. No. 14/546,406, which may provideoperational and economic advantages.

FIG. 6 shows another example HPLAPS system that comprises a highpressure turbine and a combustion turbine similarly to the examples ofFIG. 4 and FIG. 5. HPLAPS system 600 of FIG. 6 differs from the examplesof FIG. 4 and FIG. 5 by using a low temperature heat source to regasifythe pressurized liquid air, instead of regasifying the liquid air in thereheated exhaust stream from the combustion turbine. The intent is touse available but otherwise low thermodynamic potential heat as asupplement and to improve the exergetic efficiency by more closelymatching the liquid air stream temperature to the warming streamtemperature. Referring to FIG. 6, in HPLAPS system 600 liquid air ispressurized by cryopump 130 and then re-gasified in gasifier 140 usinglow temperature heat that may be from a source external to the LAPSprocess and system. For example, the low temperature heat may be drawnfrom ambient sources (e.g., ambient air) or be waste heat from anotherprocess including for example heat that had been previously captured andstored, rather than derived from the combustion turbine burner or theduct burner (although those may also be acceptable heat sources). Theregasification from an external source may also provide a coolingfunction to the external process, such as for example condensing steamfrom a steam turbine. The re-gasified air produced in gasifier 140 isfurther heated in gas heater 280 with heat from the reheated exhauststream from combustion turbine 260, and then provided to the inlet ofhigh pressure turbine 150. HPLAPS system 600 otherwise operatessimilarly to example HPLAPS systems 400 and 500 shown in FIG. 4 and FIG.5.

In HPLAPS system 600 the liquid air may be evaporated and warmed ingasifier 140 to about −20° C. to about 100° C., for example, (e.g., toabout 0° C.) before entering gas heater 280. This may prevent thereheated exhaust stream from combustion turbine 260 from being cooledbelow the dew point by heat exchange with gas heater 280, and therebyprevent the condensation of water of combustion and eliminate or reducethe need for a water separator and related equipment.

Table 1 shows the estimated performance of the HPLAPS system 600 of FIG.6 for example operating parameters.

FIG. 7 shows another example HPLAPS system that comprises a highpressure turbine and a combustion turbine similarly to the examples ofFIG. 4, FIG. 5, and FIG. 6. As in example HPLAPS system 600 of FIG. 6,HPLAPS system 700 of FIG. 7 uses gasifier 140 (also referred to hereinas “vaporizer 140”) to vaporize the pressurized liquid using lowtemperature heat, after which gas heater 280 (also referred to herein asan “air heater 280”) heated by the reheated exhaust gas stream fromcombustion turbine 260 is used exclusively for sensible heating of theregasified liquid air. HPLAPS system 700 differs from the example ofFIG. 6 by including a flue gas condenser 290 to recover heat from thewater of combustion in the exhaust gas stream, and a pre-heater 310positioned between vaporizer 140 and air heater 280 that uses heatrecovered by the condenser to pre-heat the regasified air before itenters air heater 280. Optionally, a start-up heater may be integratedinto pre-heater 310. HPLAPS system 700 otherwise operates similarly toexample HPLAPS system 600 of FIG. 6.

In HPLAPS system 700 the liquid air may be evaporated and warmed ingasifier 140 to about −60° C. to about 20° C., for example, and thenfurther heated in preheater 310 to about 50° C. to about 130° C., forexample, before entering air heater 280.

Table 1 shows the estimated performance of the HPLAPS system 700 of FIG.7 for example operating parameters.

In the examples of FIG. 6 and FIG. 7 vaporizer/regasifier 140 mayoptionally be interfaced to a thermal storage system (e.g., aconventional ice thermal storage system) used to pre-chill inlet air tothe liquefaction system, or for cooling other processes. Also,vaporizer/regasifier 140 may optionally be used as an additional oralternative heat sink for flue gas condenser 290, in which case the fluegas may be cooled for example to about 1° C., condensing more watervapor from the flue gas. In the examples of FIG. 4, FIG. 5, FIG. 6, andFIG. 7, steam may be mixed with the air and fuel in burner 270.Pressurized cooling air, for example derived from the regasified airstream, may be supplied to the hot combustion turbine section 260.Optionally, the exhaust gas from the combustion turbine and the liquidair may serve respectively as heat source and heat sink for a bottomingpower cycle, which may be for example an organic Rankine cycle.Optionally, heat rejected from the liquefaction system may be used toreheat flue gas to avoid a visible plume as shown, for example, in FIG.3 and FIG. 5.

Referring again to FIG. 7, in one variation HPLAPS system 700 isoperated to generate power by pumping liquid air from the storage tankand raising its pressure to about 150 bar, vaporizing the liquid air andwarming it to about −40° C. in gasifier 140 using heat transferred fromthe atmosphere, further warming the regasified air to about 120° C. inpre-heater 310 using heat recovered from the flue gas by flue gascondenser 310, further heating the regasified air to about 540° C. inair heater 280 using heat recovered from the reheated exhaust gas streamfrom combustion turbine 260, introducing the regasified air into highpressure turbine 150 at about 540° C. and 140 bar and expanding itthrough the high pressure turbine to exhaust at about 232° C. and about18 bar, mixing the exhaust from high pressure turbine 150 with naturalgas fuel and combusting it to form a gaseous working fluid at about1112° C. and about 17.5 bar, expanding the gaseous working fluid throughcombustion turbine 260 to exhaust at about 490° C. and a pressure ofabout 12 inches of water, reheating the exhaust gas stream from thecombustion turbine to about 551° C., and transferring heat from thereheated exhaust gas stream to regasified air in air heater 280. Theexhaust gas then exits air heater 280 at about 143° C. and flows throughflue gas condenser 310, leaving the system at about 28° C. andatmospheric pressure. Any other suitable operating parameters may alsobe used.

As shown in Table 1, overall fuel consumption in HPLAPS system 600 andHPLAPS system 700 may be reduced compared to that of HPLAPS system 300and HPLAPS system 400 by the introduction of heat from outside the LAPSsystem and by recapturing heat from the flue gas.

FIG. 8A shows another example HPLAPS system. In this example, HPLAPSsystem 800 comprises a high pressure turbine and a conventionalcombustion turbine comprising a compressor 320, a burner 270, and apower turbine (expander) 260. The inlet air to the compressor section ofthe combustion turbine is primarily or exclusively drawn in aconventional manner from the ambient environment, though in somevariations the inlet air may comprise some regasified liquid air aswell.

In one variation compressor 320 compresses the inlet air to a pressureof, for example, about 17.5 bar, after which the compressed air iscombusted with a gaseous fuel (e.g., natural gas) in burner 270 to forma hot gaseous working fluid at a temperature of, for example, about1112° C. and a pressure of, for example, about 17.5 bar. The hot gaseousworking fluid is expanded across expander 260 to generate power, andexhausted from the expander at a temperature of about 495° C. and apressure of about 1.028 bar. Cryopump 130 pumps liquid air from storagetank 120 and raises its pressure to about 150 bar. The pressurizedliquid air is vaporized and warmed to a temperature of about −40° C. ingasifier 140 using heat transferred from the atmosphere. The regasifiedair is further heated to about 120° C. in preheater 310 using heatrecovered from the flue gas by flue gas condenser 310 and then to about470° C. in air heater 280 using heat recovered from the exhaust gasstream from power turbine 260. The heated regasified air is thenintroduced into high pressure turbine (hot gas expander) 150 at about470° C. and 140 bar and expanded through the high pressure turbine togenerate power. The exhaust from high pressure turbine 150 is at or nearatmospheric pressure, rather than at an intermediate pressure as inHPLAPS systems 400, 500, 600, and 700 described above. The combustionturbine (compressor 320, burner 270, expander 260) and the high pressureexpander 150 may be conventional “off the shelf” equipment, whichreduces technical risk compared to systems requiring customizedequipment.

The exhaust from the high pressure turbine may be at a temperature wellbelow the freezing point of water. Cold may be captured from the liquidair and/or from the high pressure turbine exhaust to assist withliquefaction of air at a later time, using ice storage for example asshown in example HPLAPS system 800B of FIG. 8B. Evaporation of liquidair in vaporizer 140 requires heat, which could be provided by freezingwater or brine in ice tank 325, for example by circulating anon-freezing heat transfer fluid, such as ethylene-glycol and water,between vaporizer 140 and ice tank 325. During the charging phase, whenair liquefier 110 is operating, the heat transfer fluid could becirculated between air liquefier 110 and ice tank 325 to absorb heatrejected from the air liquefier 110, to pre-chill inlet air entering airliquefier 110, or to provide intercooling within air liquefier 110.

Table 1 shows the estimated performance of HPLAPS system 800 of FIG. 8Afor example operating parameters.

In example HPLAPS system 900A of FIG. 9A air discharged from hot gasexpander 150 flows into compressor 320 to supplement or completelyreplace ambient air. It is not necessary to have the same mass flow rateof air flow through the hot gas expander 150 and the combustion turbine.A damper 330 may be disposed between expander 150 and compressor 320 todischarge air to the atmosphere, to block inlet ambient air, and/or tomix air discharged from hot gas expander 150 with ambient inlet air.Another damper 335 may be disposed between expander 260 and air heater280 to allow exhaust gas from expander 260 to either flow through orbypass air heater 280, allowing the system to function as either anHPLAPS system or a combustion turbine. The flow rate of air throughcompressor 320 is governed by the rotational speed of the compressor,which may be fixed in the case of single shaft combustion turbines, andpressure rise, which is influenced by the temperature ratio across theexpander 260. In many cases it may be desirable for the air to bedischarged from the hot gas expander 150 at a temperature and pressureequivalent to the ISO nominal inlet conditions for compressor 320 of 15°C. and sea level atmospheric pressure. This could be achieved byincluding a duct burner to raise the temperature of air entering hot gasexpander 150 (similarly to duct burner 180 of LAPS system 700), by twoor more stages of expansion in hot gas expander 150 with reheat betweenstages, or by reducing the inlet pressure to hot gas expander 150.Slight adjustment of the hot gas expander 150 inlet pressure andtemperature may be used to compensate for the difference in compositionof the air discharged from compressor 320 compared to standard air,which includes water vapor, carbon dioxide and trace components that areremoved by air liquefier 110.

In example HPLAPS system 900B of FIG. 9B the discharge from hot gasexpander 150 is at the pressure and temperature conditions of system600, and the air flows through a damper 340 to permit the burner 270 tobe supplied from either compressor 320 or hot gas expander 150. Amechanical clutch 345 may be provided to allow power from expander 260to be supplied to compressor 320 or combined with power from hot gasexpander 150 to produce electric power. Compressor 320, expander 260,and hot gas expander 150 may rotate about a common shaft, or may beoffset, and in either case may be connected by gearing in order topermit operation at suitable rotational speeds for the respectivecomponents.

Table 1 shows the estimated performance of HPLAPS system 900A of FIG. 9Afor example operating parameters. The performance summarized in Table 1for the various example HPLAPS systems assumes that the liquefactionplant operates 14.4 hours per day in order to produce sufficient liquidair to operate the power generation plant for 5 hours per day.

TABLE 1 HPLAPS HPLAPS HPLAPS HPLAPS HPLAPS HPLAPS Parameter System 300System 400 System 600 System 700 System 800 System 900 Air Flow (kg/s)49.1 49.1 49.1 49.1 49.1 49.1 DB Fuel Flow (kg/s) 0.8822 0.2585 0.12890.075 0 0 HP Turbine Inlet Temp. (° C.) 540 540 540 540 470 470 HPTurbine Inlet Pres. (kPa) 14000 14000 14000 14000 14000 6731 HP TurbineOutlet Pres (kPa) 101.325 1800 1800 1800 101.325 101.325 HP TurbineOutlet Temp. (° C.) 2 232 232 232 −24 15 HP Turbine Power (MW) 27.4816.40 16.58 16.58 25.4 23.3 CT Fuel Flow — 1.125 1.076 1.073 0.91 0.91CT Turbine Inlet Temp. (° C.) — 1112.5 1112.2 1112.5 1112.5 1112.5 CTTurbine Inlet Pres. (kPa) — 1737.5 1737.5 1737.5 1737.5 1737.5 CTTurbine Power (MW) — 36.88 35.9 35.9 14.2 14.2 Flue Gas Temperature (°C.) 19.85 19.85 60 28 18.4 26 Condensate Flow (kg/s) 1.70229 2.79048 01.44074 1.21 .88 Heat Rate (kJ/kWh) 6105 5034.7 4499.3 4442.4 4165 4332Flue Reheat Duty (MW) 0.96 0.71 — 9.75 9.76 9.0 Preheat Duty (MW) 1.9 —16.7 13.9 13.9 13.9 Electric Energy Ratio (MWh out/in 69.5% 50.9% 52.3%CO2 emissions (kg/MWh) 222.8 216.4 225.1

This disclosure is illustrative and not limiting. Further modificationswill be apparent to one skilled in the art in light of this disclosureand are intended to fall within the scope of the appended claims.

What is claimed is:
 1. A method of recovering stored energy from liquidair or liquid air components, the method comprising: pressurizing theliquid air or liquid air components to a pressure greater than or equalto about 80 atmospheres; regasifying the pressurized liquid air orliquid air components to produce pressurized gaseous air or gaseous aircomponents at a pressure greater than or equal to about 80 atmospheresusing heat produced by combusting an exhaust gas stream from a highpressure turbine with a gaseous fuel; expanding the pressurized gaseousair or gaseous air components through the high pressure turbine to formthe exhaust gas stream; and producing electricity with a generatordriven by the high pressure turbine.
 2. The method of claim 1, whereinthe pressurized gaseous air or gaseous air components have a temperatureof about 450° C. to about 650° C. at an inlet to the high pressureturbine.
 3. The method of claim 1, wherein combustion of the exhaust gasstream from the high pressure turbine with the gaseous fuel occurs at apressure of about one atmosphere.
 4. The method of claim 1, comprisingat start-up of the method regasifying the pressurized liquid air orliquid air components to produce pressurized gaseous air or gaseous aircomponents at a pressure greater than or equal to about 5 atmospheresusing heat produced by combusting ambient air with the fuel.
 5. Themethod of claim 1, comprising producing the liquid air or liquid aircomponents in an electrically powered liquefaction process and storingthe liquid air or liquid air components for later regasification andexpansion through the high pressure turbine.
 6. The method of claim 5,comprising preheating the exhaust gas stream from the high pressureturbine with heat rejected from the liquefaction process beforecombusting the exhaust gas stream from the high pressure turbine withthe fuel.
 7. The method of claim 5, comprising reheating the exhaust gasstream from the high pressure turbine with heat rejected from theliquefaction process after regasifying the liquid air or liquid aircomponents with heat produced by combusting the exhaust gas stream fromthe high pressure turbine with the gaseous fuel.
 8. The method of claim1, wherein: the pressurized gaseous air or gaseous air components have atemperature of about 450° C. to about 650° C. at an inlet to the highpressure turbine; and combustion of the exhaust gas stream from the highpressure turbine with the gaseous fuel occurs at a pressure of about oneatmosphere.
 9. The method of claim 8, comprising producing the liquidair or liquid air components in an electrically powered liquefactionprocess and storing the liquid air or liquid air components for laterregasification and expansion through the high pressure turbine.
 10. Themethod of claim 1, comprising: expanding the exhaust gas stream from thehigh pressure turbine through a combustion turbine after combusting theexhaust gas stream from the high pressure turbine; producing additionalelectricity with a generator driven by the combustion turbine; andcombusting uncombusted gaseous air or gaseous air components in theexhaust gas stream from the high pressure turbine with additionalgaseous fuel after expanding the exhaust gas stream from the highpressure turbine through the combustion turbine; wherein the regasifyingof the pressurized liquid air or liquid air using heat produced bycombusting the exhaust gas stream from the high pressure turbine occursafter expanding the exhaust gas stream from the high pressure turbinethrough the combustion turbine and after the combusting of uncombustedgaseous air or air components in the exhaust gas stream from the highpressure turbine; and wherein the exhaust gas stream from the highpressure turbine is exhausted from the high pressure turbine at apressure of about 10 to about 25 atmospheres.
 11. The method of claim10, wherein the pressurized gaseous air or gaseous air components have atemperature of about 400° C. to about 650° C. at an inlet to the highpressure turbine, and the exhaust gas stream from the high pressureturbine has a temperature of about 1000° C. to about 1400° C. at aninlet to the combustion turbine.
 12. The method of claim 10, whereincombustion of the uncombusted gaseous air or gaseous air components inthe exhaust gas stream from the high pressure turbine after expandingthe exhaust gas stream from the high pressure turbine through thecombustion turbine occurs at about atmospheric pressure.
 13. The methodof claim 10, comprising at start-up of the method regasifying thepressurized liquid air or liquid air components to produce pressurizedgaseous air or gaseous air components at a pressure greater than orequal to about 5 atmospheres using heat produced by combusting ambientair with fuel.
 14. The method of claim 10, comprising combusting astream of ambient air with the uncombusted gaseous air or gaseous aircomponents in the exhaust gas stream from the high pressure turbine andthe additional gaseous fuel.
 15. The method of claim 10, comprisingproducing the liquid air or liquid air components in an electricallypowered liquefaction process and storing the liquid air or liquid aircomponents for later regasification and expansion through the highpressure turbine.
 16. The method of claim 15, comprising reheating theexhaust gas stream from the high pressure turbine with heat rejectedfrom the liquefaction process after regasifying the liquid air or liquidair components with heat produced by combusting the exhaust gas streamfrom the high pressure turbine with the gaseous fuel.
 17. The method ofclaim 10, wherein: the pressurized gaseous air or gaseous air componentshave a temperature of about 400° C. to about 650° C. at an inlet to thehigh pressure turbine, and the exhaust gas stream from the high pressureturbine has a temperature of about 1000° C. to about 1400° C. at aninlet to the combustion turbine; and combustion of the uncombustedgaseous air or gaseous air components in the exhaust gas stream from thehigh pressure turbine after expanding the exhaust gas stream from thehigh pressure turbine through the combustion turbine occurs at aboutatmospheric pressure.
 18. The method of claim 17, comprising producingthe liquid air or liquid air components in an electrically poweredliquefaction process and storing the liquid air or liquid air componentsfor later regasification and expansion through the high pressureturbine.